This invention relates to a protective container for printed circuit boards, and particularly to such a container in which the printed circuit boards are securely held during handling, storage, testing, shipping, as well as providing a field service container. Additionally at all times the printed circuit boards are surrounded by a Faraday Cage.
In recent years as tremendous progress has been made in the field of micro-electronics, it has become possible to miniaturize electronics increasingly through the use of integrated circuits. Such miniaturization permits more and more components to be mounted on printed circuit boards, which components utilize very small voltages. While such developments have been significant in the generation of numerous new products, certain problems have arisen which were essentially unknown in earlier electronic production practices.
One of these problem areas has been the effect of static electricity and the damage it can cause on sensitive electronic components. Static electricity is a phenomenon that occurs quite naturally and quite often in relatively dry environments through the normal activities of employees who are handling sensitive equipment. For example, static charges of a significant magnitude, enough to damage or destroy certain sensitive micro-electronic components can be generated by an individual walking across a floor, then touching sensitive equipment. At such times the charge is transferred from the person's hand to the circuitry. Further, the damage may occur without any indication thereof until the circuit is mounted into its operative environment and tested.
Thus, considerable effort has been undertaken to prevent such damage. It is now known that once such sensitive components are assembled onto a printed circuit board, the printed circuit board should remain protected, as much as possible, within a Faraday Cage. A Faraday Cage is generally a container formed of a conductive polymeric material which surrounds and isolates the sensitive equipment from such charges.
Printed circuit boards are made in a variety of sizes, but are generally rectangular. During manufacture, printed circuit boards undergo several separate operations. First, the circuit pattern is etched and printed on one or both sides of a carrier or substrate. Next, components are mounted in holes therein either by automatic insertion or by hand. The components are subsequently secured in place by a soldering technique such as wave or vapor soldering, and later the boards may be assembled into a panel, drawer, or the like with other similar printed circuit boards or electrical components. At various stages of this manufacturing process, the printed circuit boards must be stored or transported to another manufacturing area. Once the sensitive components are inserted onto the boards, the boards must thereafter be protected from static charges, as well as being protected from physical damage. All of these procedures require multiple handlings between the operative steps.
After the components are initially mounted on the printed circuit boards and before they are soldered, there is generally some handling and storage necessary. After wave soldering, the boards must be somehow suspended in an air path for drying. Once the assembly and soldering operations have been completed, there is generally a testing procedure conducted. The boards are then stored or shipped to the field, and often in the field must be stored for a period of time before utilization in some type of larger assembly. During all of these operations it is important that the sensitive components on the printed circuit boards be protected from electrostatic charges. Thus during such storage and handling operations, the less the boards have to be removed, the better.
Early approaches to this problem resulted in the printed circuit boards being wrapped in some type of high surface resistant, groundable bags or wrappers. Later, cartons or boxes were developed in which the surfaces thereof were coated with an electrically conductive material. Handling trays and shipping cartons formed of a metallic or electrically conductive polymeric material have now been developed in which the printed circuit boards are vertically mounted in slots or grooves in the walls of such containers. Examples of such types of protective carriers which have evolved include those shown and described in U.S. Pat. Nos. 4,211,324 to Ohlbach; 4,404,615 to Dep; 4,426,675 to Robinson et al; 4,427,114 to Howell et al; and 4,480,747 to Kazor et al.
None of the approaches set forth above are completely satisfactory for one reason or another. For example, none of the approaches permit a printed circuit board to be stored before the components are soldered in place (not mounted in a horizontal plane); none of the approaches permit drying and testing while the printed circuit boards are maintained within the container; and none of the approaches permit easy access to printed circuit boards maintained in stacked carriers. Further, none of the approaches known to the applicants have been designed for loading and unloading of printed circuit boards into the carriers by simple robotic motion. In short, each of the approaches known to the applicant are limited for use either as shipping containers or as temporary storage containers, and require repeated removal and replacement, of the printed circuit board. Each removal breaks the Faraday Cage, and thus requires reestablishment thereof and protection while out of the container.